The process of electrostatographic copying, as originally disclosed by C. F. Carlson in U.S. Pat. No. 2,297,691, involves the uniform electrostatic charging of a layer of photoconductive material dispersed on a conductive substrate with subsequent exposure of the charged layer to light and shadow to selectively discharge the photoconductive layer and thereby form a latent electrostatic image on the surface of the layer corresponding to the shadow areas. The latent image is developed by contacting the layer with a particulate electroscopic marking material, commonly referred to as toner, which adheres to the non-discharged areas and can be transferred to a receiving member such as paper in imagewise configuration.
The conductive substrate and layer of photoconductive material, which normally contains a resistive barrier layer between the substrate and photoconductive material and may have a protective overcoating on the surface of the photoconductive layer, is generally referred to as the photoreceptor. Typically, the photoconductive material used in photoreceptors is amorphous selenium or an alloy thereof. As is well known, amorphous selenium and selenium alloy photoreceptors are sensitive materials, being easily scratched or electrically affected by foreign objects or human hand contact.
Photoreceptors are easily damaged in field use such as by paper scratching and handling damage which may occur when the photoreceptor is installed or serviced. In addition, foreign matter such as paper clips may come into contact with the photoreceptor during the copying process and gouge the layer of photoconductive material. The damaged photoreceptor is left with depressions on its surface which reduce copy quality. In the case where the depression is deep enough so as to protrude through the photoconductive material to the conductive substrate, the damaged area cannot hold a charge and will not contribute to the formation of the latent image. Less severe scratches which do not form depressions through the entire thickness of the photoconductive layer may be revealed on the finished copy. Copy quality can be reduced initially since the photoconductive material remaining in the damaged area may have a contrast potential less than the sensitivity of the system. In addition, as the imaging and development cycle is repeated, toner particles tend to build up in the depressions since ordinary photoreceptor cleaning techniques are effective in removing toner only when it is on a relatively smooth surface. The buildup of toner particles, which are normally non-conductive, results in damaged areas retaining their charge during exposure and thereby forming part of the latent image. These areas are developed along with the rest of the latent image and ultimately show up as dark areas when the toner is transferred from the photoreceptor to the paper.
As the photoreceptor receives progressively more scratches, it reaches a point where copy quality is unacceptable whereupon it must be replaced or repaired with the latter option obviously being preferred. One method of repairing selenium based photoreceptors involves buffing the damaged areas to physically remove the depression by abrading away the photoconductive material in the scratched area down to a thickness commensurate with the total layer thickness less the depth of the depression. While various polishes and buffing agents have been utilized in selenium repair they have been found unsatisfactory for many reasons. Some are too abrasive resulting in damage to the affected area of application. Others contain constituents which leave a film on the selenium photoreceptor surface resulting in an electrostatically occluded area. Additionally, some buffing compositions required more than ordinary technique and care thereby rendering them unsatisfactory for field application, i.e., in offices and any other places where copiers are placed.
In copending application Ser. No. 512,803 now U.S. Pat. No. 3,971,169, and 512,804 now U.S. Pat. No. 3,959,934, both filed on Oct. 4, 1974 there is disclosed an abrasive composition which overcomes many of the disadvantages noted above. The compositions disclosed primarily utilize feldspar as the abrasive additive. The present invention relates to the use of a particular abrasive of distinct particle size which improves on the compositions of the copending applications.